1. Field of the Invention
The present invention relates in general to direct fuel injection spark ignition internal combustion engines, and more particularly to the engines of a type that has a control system for controlling a fuel injection timing and an ignition timing in accordance with an operation condition of the engine.
2. Description of the Related Art
In order to clarify the task of the invention, two known engines of the above-mentioned type which have been hitherto proposed or put into practical use will be briefly described, which as are shown in Japanese Laid-open Patent Applications (Tokkai) 2001-336467 and 2003-113717.
The former describes one measure in which when a catalytic converter in an exhaust system of the internal combustion engine is not sufficiently heated, the fuel injection is carried out on the compression stroke and at the same time the ignition timing is retarded with respect to a top dead center (TDC) on the compression stroke.
The latter describes the other measure in which, during the compression stroke, a fuel injected from each fuel injector is reflected by a top of the piston to be directed toward the electrodes of the spark plug. Actually, the crown portion of the piston is so shaped as to promote such fuel reflection.
As is known in the art, in order to accelerate or promote the activation of the catalytic converter after cold starting of the engine, it is preferable to increase the temperature of the exhaust gas, and in order to reduce HC (hydrocarbons) in the exhaust gas, it is preferable to largely retard the ignition timing. However, if the ignition timing is too retarded, a combustion stability of the engine is deteriorated and thus retarding of the ignition timing has inevitably a limitation. Thus, it is difficult to obtain a stable combustion especially when the engine is not sufficiently warmed up. Actually, the limited ignition timing determined based on the stable combustion is at a relatively advanced side and thus, usually, sufficient retarding of the ignition timing is not practically made.
In the measure disclosed by the publication 2003-113717, the crown portion of the piston is formed with a recess of which bottom surface constitutes a parabolically concave surface. The concave surface is so shaped as to have a focus at electrodes of a spark plug at the time when a fuel is injected from a fuel injection valve. However, in the period before the fuel injection on the compression stroke, the moving speed of the piston is quite high and thus practically, the period for which the focus of the concave bottom surface of the recess of the piston is kept placed at the electrodes of the spark plug is very short. Thus, the combustion stability of the engine is affected severely by the fuel injection period.
It is therefore an object of the present invention to provide a direct fuel injection spark ignition internal combustion engine, which is free of the above-mentioned drawbacks.
As will become apparent from the following description, in accordance with the present invention, the following measures are practically employed to solve the above-mentioned drawbacks.
That is, when the engine is in a predetermined operation condition, such as a condition just after cold starting, the control is so made that the fuel injection starts at a time before the top dead center (TDC) on the compression stroke and ends at a time after the top dead center (TDC) on the compression stroke, and the ignition of the injected fuel is carried out at a time after the top dead center (TDC) on the compression stroke. Furthermore, the crown portion of the piston is so shaped that when the piston comes to the top dead center (TDC) on the compression stroke, a fuel injected from the fuel injector can be reflected by the crown portion to be directed toward electrodes of a spark plug.
In accordance with a first aspect of the present invention, there is provided a direct fuel injection spark ignition internal combustion engine which comprises a cylinder; at least one intake port leading to the cylinder; at least one exhaust port extending from the cylinder; a piston axially movably received in the cylinder to define in the same a combustion chamber that is connectable with the intake and exhaust ports through intake and exhaust valves respectively; a fuel injection valve having a fuel injection nozzle exposed to the combustion chamber; a spark plug having electrodes exposed to the combustion chamber; an arrangement wherein when, with the piston assuming the top dead center on the compression stroke, a fuel is injected from the nozzle of the fuel injection valve, the injected fuel from the nozzle is guided to reach the electrodes of spark plug by a crown portion of the piston; and a control unit that controls the fuel injection valve and the spark plug, the control unit being configured to carry out under a given condition controlling the fuel injection valve to start the fuel injection at a time before the top dead center (TDC) on the compression stroke and finish the fuel injection at a time after the top dead center (TDC) on the compression stroke; and controlling the spark plug to carry out the ignition at a time after the top dead center (TDC).
In accordance with a second aspect of the present invention, there is provided a direct fuel injection spark ignition internal combustion engine, which comprises an arrangement wherein when, with a piston assuming the top dead center (TDC) on the compression stroke, a fuel is injected from a nozzle of a fuel injection valve, the injected fuel from the nozzle is guided to reach electrodes of a spark plug by a concave surface defined by a crown portion of a piston; and a control unit that controls the fuel injection valve and the spark plug, the control unit being configured to carry out under a given condition controlling the fuel injection valve to start the fuel injection at a time before the top dead center (TDC) on the compression stroke and finish the fuel injection at a time after the top dead center (TDC) on the compression stroke; and controlling the spark plug to carry out the ignition at a time after the top dead center (TDC).
In accordance with a third aspect of the present invention, there is provided a method of operating a direct fuel injection spark ignition internal combustion engine which comprises a cylinder; at least one intake port leading to the cylinder; at least one exhaust port extending from the cylinder; a piston axially movably received in the cylinder to define in the same a combustion chamber that is connectable with the intake and exhaust ports through intake and exhaust valves respectively; a fuel injection valve having a fuel injection nozzle exposed to the combustion chamber; a spark plug having electrodes exposed to the combustion chamber; and an arrangement wherein when, with the piston assuming the top dead center (TDC) on the compression stroke, a fuel is injected from the nozzle of the fuel injection valve, the injected fuel from the nozzle is guided to reach the electrodes of spark plug by a crown portion of the piston. The method comprises controlling the fuel injection valve to start the fuel injection at a time before the top dead center (TDC) on the compression stroke and finish the fuel injection at a time after the top dead center (TDC) on the compression stroke; and controlling the spark plug to carry out the ignition at a time after the top dead center (TDC).